1. The Field of the Invention
The present invention relates to the manufacture of endodontic instruments. More particularly, the invention relates to a metal powder sintering process and a cold forming process for manufacturing endodontic files.
2. The Relevant Technology
When a root canal of a living tooth becomes infected or abscessed, discomfort and, in many cases, severe pain can result. In the early days of dentistry the only solution was to pull the tooth. More recently, however, dental practitioners have learned to successfully remove the pulp material forming the nerve of the tooth that has become infected and, after careful preparation of the canal that contained the nerve material, refill the canal with an inert filling material, such as gutta percha, permitting a patient to retain the tooth.
To achieve a successful root canal restoration, the dental practitioner must carefully and, as completely as possible, remove the infected pulp material of the tooth to prevent continued or future infection of surrounding tissues. The removal process typically includes shaping the root canal so that it can be effectively and successfully filled and sealed with an inert material. Filling and sealing minimizes the possibility of further infection occurring within the cleaned and shaped root canal.
Cleaning and shaping the root canal in preparation of sealing and filling the root canal is achieved by the use of metal files. The metal files have cutting surfaces for removing tissue in the root canal. The cutting surfaces are typically formed by helical flutes formed in the file. One or more helical cutting surfaces may be provided, which may be axially spaced as desired.
Some existing endodontic instruments and manufacturing methods are described in U.S. Pat. No. 4,934,934, U.S. Pat. No. 5,653,590, and U.S. Pat. No. 5,762,541.
Since root canals are seldom straight, often having bends and twists, at least some endodontic files are advantageously flexible. Currently preferred materials of construction include stainless steel, and more recently, nickel-titanium (Ni—Ti) alloys. Such materials, especially Ni—Ti alloys, exhibit good flexibility, resilience and strength, and are not likely to fail during use. Flexibility and strength are important to avoid file breakage during the cleaning process.
Current methods of manufacturing metal endodontic files require time intensive and costly methods. For example, stainless steel endodontic files are typically machined to form a cutting edge and then twisted to make a flute along the file's axis.
Another existing method of manufacturing existing endodontic files uses a grinding technique to form a cutting edge. In the grinding operation, a metallic (typically a titanium alloy) rod is advanced past a rotating grinding wheel at a relatively slow feed rate. The depth of cut may be varied along the length of the rod to produce a tapered endodontic file having a helical flute. Such a method is disclosed in U.S. Pat. No. 5,762,541.
While current manufacturing methods are capable of producing endodontic files in a variety of different shapes and sizes using a variety of different metals, there is still a great need to reduce the costs of manufacturing endodontic files. Forming an endodontic file from raw materials is currently a significant expense in the endodontic manufacturing process. One problem with current processes is the time it takes to form each piece. For example, forming a cutting edge by grinding a metal wire can take more than a minute for each piece and the grinding machine can cost hundreds of thousand of dollars.
Another problem with endodontic manufacturing processes is they fail to reduce or sometimes cause stress fractures or weaknesses in the metal of the file. Even minor imperfections in the metal of an endodontic file can be problematic. Endodontic files are very thin, thus small imperfections can cause the file to break during use. A broken file in a root canal is very difficult to remove and can cause damage to the root canal.
Therefore, what is needed is a manufacturing process that can reduce the cost of manufacturing endodontic files while maintaining or improving the strength of the endodontic file.